Topic Contents

Genetic Test

Test Overview

A genetic test examines the
DNA (deoxyribonucleic acid) of a person's cells.
Genetic testing can identify changes in
genes or can analyze the number, arrangement, and
characteristics of the
chromosomes. Testing may be performed on samples of
blood, semen, urine, saliva, stool, body tissues, bone, or hair.

You inherit half of your genetic information from your mother and the
other half from your father. Genes, alone or in combination, determine what
features (genetic traits) a person inherits from his or her parents, such as
blood type, hair color, eye color, and other characteristics, including risks
for certain diseases. Certain changes in genes or chromosomes may
cause medical problems.

Why It Is Done

A genetic test is done to:

Find out if people who have a
family history of a specific disease are likely to pass that disease on to
their children (carrier identification). Information
obtained from this type of testing can help guide a couple as they make
decisions regarding pregnancy.

Find out if a
fetus has a disorder such as
Down syndrome (prenatal testing). Information obtained from this type of testing can help guide
a couple as they make decisions regarding pregnancy.

Check for
various metabolic diseases, such as
phenylketonuria (PKU) (newborn screening). Information obtained from newborn screening can help guide
medical treatment to ensure the best possible outcome for the
baby.

Check to see if you carry a genetic change that increases your
risk for a disease, such as breast cancer or
Huntington's disease, later in life (late-onset disease testing). This might be important to you if
you have a parent or other relative diagnosed with the disease. Information
obtained from this type of testing can help you make decisions about disease
prevention or future childbearing.

Help diagnose hypertrophic cardiomyopathy (HCM) or screen for HCM in close relatives of a person who has the disease.

Check for genetic changes that may affect your treatment for
diseases such as
HIV or some cancers.

Check for a genetic change that may affect how a medicine, such as clopidogrel, will work.

How To Prepare

You do not need to do anything before you have this test.

Talk with your doctor about any concerns you have
regarding the need for the test, its risks, how it will be done, or what the
results will mean. To help you understand the importance of this test, fill out
the
medical test information form(What is a PDF document?).

Since the information obtained from a
genetic test can have a profound impact on your life, you may want to see a
doctor who specializes in genetics (geneticist) or a
genetic counselor. This type of counselor is trained
to help you understand your risk for developing a genetic disease or having a
child who has an inherited (genetic) disease, such as
sickle cell disease,
cystic fibrosis, or
hemophilia. A genetic counselor can help you make
well-informed decisions. Ask to have genetic counseling before making a
decision about genetic testing.

How It Is Done

A genetic test can be done using almost
any cell or tissue from the body.

Blood sample from a heel stick

If genetic testing
is done on a baby, a heel stick usually is done instead of a blood draw from a
vein. For a heel stick blood sample, several drops of blood are collected from
the heel of the baby. The skin of the heel is cleaned with alcohol and then
pricked with a small, sterile lancet. Several drops of blood are collected
inside circles on a specially prepared piece of paper. When enough blood has
been collected, a gauze pad or cotton ball is placed over the puncture site.
Pressure is applied to the puncture site briefly, and then a small bandage is
usually placed over it.

Blood sample from a vein

The health professional
drawing your blood will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Apply a gauze pad or cotton ball over the needle site as
the needle is removed.

Cell sample from a fetus

How It Feels

Blood sample from a heel stick

The baby may feel a
brief sting or a pinch when the lancet pricks the skin. While the blood is
being collected, there is very little or no discomfort.

Blood sample from a vein

You may feel nothing at
all from the needle puncture, or you may feel a brief sting or pinch as the
needle goes through the skin. Some people feel a stinging pain while the needle
is in the vein. But many people do not feel any pain, or they have only minor
discomfort, after the needle is positioned in the vein. The amount of pain you
feel depends on the skill of the health professional drawing the blood, the
condition of your veins, and your sensitivity to pain.

The collection of DNA from saliva, urine, or semen
does not cause discomfort.

Risks

Blood sample from a heel stick

There is very
little risk of complications from having blood drawn from a heel stick. A small
bruise may develop at the puncture site.

Blood sample from a vein

There is very little risk
of complications from having blood drawn from a vein.

You may get a small bruise at the
puncture site. You can lower the chance of bruising by keeping pressure on the
site for several minutes.

In rare
cases, the vein may become swollen after the blood sample is taken. This
problem is called phlebitis. A warm compress
can be used several times a day to treat this.

Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

There are no risks linked with collecting DNA from
saliva, urine, or semen.

Other factors

The information obtained from a
genetic test can affect your life and the lives of your family in many ways,
including:

Psychological effects. The emotions you
may experience if you learn that you are likely to develop a serious disease or
have an affected child can cause you to feel anxious or depressed. This
information may also affect your relationship with your partner or other family
members.
Genetic counseling is recommended before you have
genetic testing.

Medical treatment choices.
If you test positive for a disease-specific gene change (mutation), you may decide to use
preventive or treatment options, if they are available, to reduce the impact or
severity of the disease. While many treatment options have been proved effective,
others may be potentially dangerous or of unproven
value.

Pregnancy decisions. Finding out that your
unborn child (fetus) is or may be affected by a genetic disease can impact the
decisions you make about the pregnancy. You may want to consider ending the
pregnancy. Or you may need to change your delivery plans. If you had planned on
giving birth at home, you may need to have your baby in a hospital. If your
child is likely to need special care after birth, you may need to deliver in a
hospital other than the one you first chose. You may also need to have special
health professionals present at the birth.

Privacy issues. Many people worry that genetic
information released to insurance companies may affect future employment
options or the cost or availability of insurance. But a law in the United
States, called the Genetic Information Nondiscrimination Act of 2008 (GINA),
protects people who have DNA differences that may affect their health. GINA
prevents employers and health insurance companies from using DNA information
about people to affect decisions. This law does not cover life insurance,
disability insurance, or long-term care insurance.

Results

A genetic test examines the
DNA (deoxyribonucleic acid) of a person's cells.
Genetic testing can identify changes in
genes or can analyze the number, arrangement, and
characteristics of the
chromosomes.

The results of genetic
testing depend on the type of test done. Genetic testing is used to:

Diagnose an inherited
disease.

Provide information about how likely it is that you will
develop a disease in the future.

Determine whether you are a
carrier of the disease.

Provide information about the severity of
an inherited disease.

Help choose appropriate treatment for some
diseases, such as
HIV infection or some types of cancer.

What Affects the Test

Having a blood transfusion
within a week before the test can interfere with your test or the accuracy of
the results.

What To Think About

The information obtained from a
genetic test can have a profound impact on your life. Genetic counselors are
trained to help you understand your risk for having a child with an inherited
(genetic) disease, such as
sickle cell disease,
cystic fibrosis, or
hemophilia. A
genetic counselor can help you make well-informed
decisions. Ask to have
genetic counseling before making a decision about
genetic testing.

A genetic test result is sensitive information.
Your confidentiality should be maintained, and the release of information
should be limited to those who are authorized to receive it.

The discovery of a genetic disease that is not causing symptoms
now (such as breast cancer or Huntington's disease) should not affect your
future ability to gain employment or health insurance coverage. A law in the
United States, called the Genetic Information Nondiscrimination Act of 2008
(GINA), protects people who have DNA differences that may affect their health.
This law does not cover life insurance, disability insurance, or long-term care
insurance.

A genetic test can
sometimes reveal unintended information, such as the identity of a child's
father (paternity).

A
fetal genetic test may detect a serious disease or disorder (such as
Down syndrome) that will greatly impact your child's
life and the lives of caregivers. A pregnant woman who is considering genetic
testing may want to consider her ethical, social, and religious beliefs to help
her determine the actions she would take if test results are positive.

A karyotype can be used to examine the size, shape, and number of
chromosomes. Extra or missing chromosomes, or abnormal positions of chromosome pieces, can
cause problems with a person's growth, development, and body functions. To learn more, see the topic
Karyotype Test.

A type of genetic test (DNA fingerprinting) can be used to
determine paternity, help solve crimes, and identify a body. DNA fingerprinting
is more accurate than dental records, blood type, or traditional fingerprints.
To learn more, see the topic
DNA Fingerprinting.

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